I recently purchased some Arion HS-500 amps:
http://www.arionaudio.com/HS_500.pdf
The guy that got them in for me uses Mac 501's as his reference amp and nothing in the past had really been able to show it a clean pair of heels. I went down to really give them a good listen and see what difference putting in a Duelund capacitor would make - its uses a Cardas Golden Ratio as the capacitor coupling the valve input stage and the digital output stage. Its a good capacitor but the Duelund should easily best it.
Using some new speakers the person whose system we heard it on had developed (they are very very transparent easily being the best speakers I had ever heard - I got a pair virtually on the spot - but that's another story) me and a couple of other guys did a comparison to the Mac 501's. On some material we felt the Mac's were better, and on others the Arion's. That was a consensus view - I personally preferred the Arion's on all material - more real sounding and organic to my ears. Now the Duelund was put in. Bloody hell - it now smoked the Mac's on all material - clearer, cleaner, faster, purer, but still very organic - awesome sound. It exposed the Mac's weaknesses bare - the thought was it was the transparency of the new speakers that allowed it to be so easily heard.
With the Duelund no amp I have ever heard can touch this thing - and its not even run in yet - its supposed to improve considerably with run in. In fact the guy that makes them doesnt even like people to hear them not run in for at least 200 hours.
Anyway they are being run in right now and can hardly wait until that finished - they should be AWESOME.
After hearing this comparison I wouldn't even consider 501's - especially taking into the price difference. But do get the coupling capacitor changed to a Duelund VSF Copper by a competent tech - which the guy that did it for me at the listening session was.
Thanks
Bill